The disclosure concerns an inkjet printer to print to a recording material, in particular a high-speed printer for printing web-shaped recording materials or individual pages.
In inkjet printers, print images are printed onto a recording material via targeted ejection of ink droplets or a continuous ink stream. For this a hydraulic pressure is generated in a print head that is provided with one or more ink nozzles, whereby ink droplets or the ink stream are/is ejected from respective nozzle channels. In inkjet printers it is typical that the print head moves relative to the recording material during the printing. For this the print head and/or the recording material can be moved accordingly.
The ink for printing is drawn from a reservoir and is possibly supplied via one or more intermediate containers to the print head or heads. The ink in the print head is placed under high pressure so that the ink droplets or the ink stream can be ejected. Such strong pressure fluctuations can trigger cavitation. Small gas bubbles are thereby formed. Since gas bubbles are compressible in the print generation, a reproducible droplet formation or stream formation is then no longer ensured. The ink should therefore be largely degassed before being supplied to the print head.
A degassing device is known from the document WO 2006/029236 A1. The ink to be degassed is thereby drawn from an intermediate container, degassed and supplied again to the intermediate container. The gas that arises is discharged. During the extraction of the ink, the ink can be mixed with the aid of a stirrer (an agitator) so that no regions with increased amounts of degassed ink and increased amounts of ink that has not been degassed form in the ink. The goal is that optimally little gas is dissolved in the ink as soon as it arrives at the print head.
However, the degassing in the known device is conducted only during print pauses. During this time period only the stirring process also proceeds. It is thus prevented there that the ink droplet generation is not negatively affected. However, if printing takes place continuously, or if long print jobs are printed—as is typical in high-capacity printers—it can occur that ink is not effectively degassed, and therefore unwanted cavitation can form.
A mixing device for an ink container in which a conventional stirrer should be replaced is known from the document U.S. Pat. No. 6,863,386 B2. To mix the components of the ink that are filled into the ink container, an inlet nozzle is arranged angled by 90° to the floor of the container. An outlet opening is arranged on the floor, downstream of an ink flow generated by the nozzle. To mix the ink, a pump is activated that draws the ink via the outlet opening and ejects the ink approximately horizontally and approximately tangential to the container edge via the inlet nozzle. A circular flow is thereby created. After the ink is uniformly mixed, it can be conducted to a filter or directly to a print head. With such a device the ink is essentially stirred only in a horizontal plane, but not the entirety of the ink in the container.